1. Field of the Invention
The present invention relates to an article of ammunition which includes an antenna for satellite navigation.
2. Discussion of the Prior Art
A munition article of that kind is known from WO 99/02936 A2 in the form of a droppable bomb with sandwich-like or patch-like satellite antenna arranged in the centre of its tail. During the dropping movement into the target area the spherical antenna characteristic thereof maintains contact with navigation satellites which are above the horizon, in order to increase the bomb hit accuracy by means of final phase control, more specifically by comparison between the target point which is predetermined in terms of co-ordinates and the geodetic actual position of the munition article.
Such an antenna configuration is however unsuitable for munition articles in the form for example of artillery shells. For, during the major part of the extended ballistic flight, the antenna directional characteristic which is oriented rearwardly from the tail antenna substantially symmetrically with respect to the longitudinal axis of the projectile would be directed approximately to the horizon, and initially even therebelow, and only slightly thereabove after the apogee. As a result there is a rather low level of probability of being able to receive a plurality of navigation satellites simultaneously with a sufficient level of freedom from interference for rapid and precise trajectory point determination, for the purposes of trajectory correction. Even the incorporation of such a patch antenna into the tip of the projectile would be unsatisfactory because its spherical characteristic which would then be oriented coaxially forwardly would be directed markedly above the horizon only in the very first phase of the ballistic trajectory, in order to be able to detect a plurality of satellites in an appropriate configuration; while the tip, after passing through the apogee, is even directed towards the ground and with such an antenna it would then be possible at best to pick up the very interference-afflicted ground reflections of the signals from navigation satellites, the processing of which sufficiently quickly results in usable items of 1navigation information, if at all, only by way of considerable signal processing complication and involvement.
Furthermore, in the case of a munition article in the form of an item of artillery munition, in view of the antenna characteristic which is not ideally spherical in practice, the problem of stabilisation rotation arises. For, with an antenna characteristic which is not circular in cross-section, the consequence of the spin which occurs upon launch from a rifled barrel is that the received satellite signals are modulated in dependence on rotation, and that severely adversely affects evaluation of the signals from a plurality of satellites in immediate succession, which signals are to be compared together in rigid phase relationship in themselves for positional determination purposes.
In consideration of those factors the object of the present invention is therefore that of providing a munition article which is fired in the manner of an artillery projectile along a substantially horizontally extended trajectory with an antenna which has an appropriate directional characteristic for the reception of items of satellite navigation information.
In accordance therewith a round-slot antenna opens into the peripheral surface of a hollow-frustoconical portion of the projectile fuse tip. The slot thereof extends transversely with respect to the axis of the cone configuration and the projectile, in the form of a radial annular disc, through the wall of the hollow-frustoconical portion. In order to promote in front of the peripherally extending slot and thus in the space around the hollow-frustoconical portion, a toroidal or torus-like electromagnetic radial reception characteristic which is possibly set somewhat forwardly, arranged at a radial spacing relative to the inner slot opening, oriented transversely with respect to the slot and thus coaxially with the longitudinal axis, are a cylindrical metal reflector wall and between same and the inner slot opening a hollow space or cavity which is closed metallically, that is to say by means of a cover plate and a bottom plate, in both axial directions. For connecting that antenna to a receiving circuit, there are feed lines at positions which are equidistantly displaced relative to each other along the peripherally extending slot, which are connected in a two-pole mode, preferably being coaxial cables, with their outer and inner conductors respectively, to the two mutually axially oppositely disposed edges of the inner slot opening which opens into the hollow space or cavity. For that purpose the feed cable at that respective coupling-out location is passed in substantially parallel relationship with the axis through the bottom plate of the hollow space or cavity along the inside peripheral surface of the outer wall of the hollow-frustoconical portion and into same.
The hollow space or cavity is divided transversely with respect to the longitudinal axis in order to be able to insert a ring comprising a material which is as poor an electrical conductor as possible, of increased dielectric constant, which independently of frequency and temperature as much as possible is also distinguished by low dielectric losses and a high level of creep or tracking resistance, such as fluorine-bearing polymer PTFE (polytetrafluoroethylene), which is on the market under trade names such as Teflon, Fluon or Hostaflon. Such an insert ring makes it possible to provide for adaptation of the electrical tuning of the hollow space or cavity to the satellite frequencies.